1. The Field of the Invention
This invention relates to spools and reels for receiving stranded materials, and, more particularly, to novel systems and methods for producing plastic flanges for reels and spools as take-up of electrical wire during manufacture.
2. The Background Art
Spools and reels have suffered from a lack of intelligent application of technology for many years. Spools date back hundreds if not thousands of years. Wooden spools and reels have been used in the textile industry as well as various electrical industries for many years with almost no innovation in their structures. Some use of plastic materials began a few decades ago. Nevertheless, manufacturing techniques continue to fall short of implementing all of the principles of engineering that are available.
Manufacturing techniques tend to focus on the simplicity of manufacture, and the simplicity of design, rather than the optimization of strength, weight, stiffness, non-catastrophic failure modes, and the like. Some of these latter considerations have been found to be significant in the manufacture and use of plastic spools and reels. Accordingly, developments by Applicant have provided improved methods for providing spools and reels having substantially reduced weight with improved stiffness and cost. Moreover, failure modes are available to provide xe2x80x9cgraceful degradationxe2x80x9d of performance rather than catastrophic failure of spools and reels in situations such as the dropping of loaded reels or spools.
Spools and reels are used in many industries. However, in the wire and cable industry, the comparative weight of stranded material on a reel or spoon is greater than others of similar size in other industries. Fracture of flanges near an outer diameter thereof is common if dropped. Likewise, due to the conventional shapes of central tubes (hubs, cores, etc.), the junctions with flanges are not inherently resistant to fracture from impact loads caused by dropping. Dropping from a working bench is common for reels and spools. Manufacturing processes for manufacturing reels and spools, as well as manufacturing processes for wire and other stranded materials, typically compels smooth circumferential edges at the outermost diameter of a flange. Accordingly, a spool not retained on an arbor during use (using the wire, rather than manufacturing and taking up the wire) may roll easily across any flat surface. Thus, while a spool or reel is considered tare weight in shipping wire and cable, and a disposable item whose cost is to be minimized a spool or reel must function reliably and durably during its entire useful life.
Otherwise, a substantial length of stranded material may be damaged beyond use. The material held on a spool or reel having a value of a few dollars may itself have a value of one thousand times the cost of a spool. A value two orders of magnitude greater than that of the spool is routine for wire of common usage.
3. State of the Art
Stranded materials, upon manufacture, are typically taken up directly onto a reel or spool. The take-up spool or reel receives the strand directly from the last step in the manufacturing process. Thereafter, the filled spool is effective for storage and handling purposes. Upon sale or distribution, the spool is often placed on an arbor, either alone or with other spools, for convenient dispensing of the linear or stranded material. Linear or stranded materials include electrical wire whether in single or multiple strands and cable (comprising multiple wires), rope, wire rope, hose, tubing, chain and plastic and rubber profile material (generally any polymeric or elastomeric extruded flexible material).
In general, a host of elongate materials as diverse as pharmaceutical unit dose packages, fiberoptic line and log chains are stored on spools. Likewise, ribbon, thread and other stranded materials are wrapped on spools.
The requirement for a spool in the manufacture and handling of wire is substantially different from spools in the textile industry. For example, the weight of wire is several times the weight of thread or rope. The bulk of wire, which translates to the inverse of density, is substantially lower for wire than for hose, tubing or even chain.
Meanwhile, most spools are typically launched on a one way trip. The collection and recycling of spools is hardly worth the effort, considering that their materials are not easily recyclable.
In the art, a typical spool has a tube portion extending between two flange portions positioned at either end of the tube portion. A spool may have a rounded rim or rolled edge at the outermost diameter. This rim serves structural as well as aesthetic and safety purposes. Spools may be manufactured in a variety of tube lengths. Each flange is fitted by some fixturing to one end of the tube and there retained. Details of spools are contained in the U.S. Pat. No. 5, 464, 171 directed to a mating spool assembly for relieving stress concentrations, incorporated herein by reference.
The impact load of a spool of wire dropping from a bench or other work surface to a floor in a manufacturing environment is sufficient to fracture the spool in any of several places. Fracture may damage wire, preclude removal, or release the wire in a tangled, useless mass.
Spools may break at the comer where the tube portion meets the flange portion or may fracture at an engagement portion along the tube portion. Spools may break near the comer between the flange and the tube portion where a joint bonds or otherwise connects the tube portion to the flange portion.
Spools and reels experience significant breakage during drop tests when manufactured in styrene or styrene-based plastics such as ABS. Polyolefins are very tough materials. Tough means that a material can tolerate a relatively large amount of straining or stretching before rupture. By contrast, a material which is not tough will usually fracture rather than stretch extensively. As a result, when a reel of wire is dropped, the energy of impact breaks the spool.
Polyolefins, by contrast, may actually be drawn past yielding into their plastic elongation region on a stress-strain chart. Polyolefins thus elongate a substantial distance. The result is that olefinic plastics will absorb a tremendous amount of energy locally without rupture. Thus, the wire on a spool which has been dropped does not become a tangled mat of loops.
Given their toughness, olefinic parts will bend, strain, distort, but usually not break. Nevertheless, olefinic plastics are not typical in the art of wire spools. Polyolefin parts are not bonded into multi-piece spools. However, lack of a solvent is one problem, lack of a durable adhesive is another. Therefore, any spool would have to be manufactured as unit of a specific size. The inventory management problem created by unique spools of various sizes is untenable, although the cost of some olefinic resins is lower than that of styrene-based resins.
Moreover, the cycle time of molds directly related to material properties is usually much faster for styrene-based resins. The designs available use wall thicknesses which result in warpage as well. All these factors, as well as others, combine to leave olefinic resins, and bonded parts made therefrom, largely unused in the spool industry.
In drop tests, a spool may be dropped axially, radially or canted off-axis. In a radial drop, spools that break typically fail near the middle of the length of the tube. In axial drops, flanges may separate from tubes in failed spools. In an off-axis drop, flanges typically fracture, and may separate from tubes, releasing wire.
Large spools are typically called reels in the wire industry. Heavy-duty reels of 12 inches in diameter and greater (6 feet and 8 feet are common) are often made of wood or metal. Plastic spools of 12-inch diameter and greater are rare and tend to be very complex. The rationale is simple. Inexpensive plastics are not sufficiently strong or tough to tolerate even ordinary use with such a large mass of wire or cable wrapped around the spool.
Moreover, large flanges for reels are very difficult to manufacture. Likewise, the additional manufacturing cost of large spools is problematic. High speed molding requires quick removal after a short cycle time. Flanges are typically manufactured to have very thick walls. Increased thicknesses directly lengthen cycle times. Thus, designs do not scale up. Therefore, the flanges have very slow cooling times and molding machines have low productivity in producing them.
Styrene plastic is degraded by recycling. That is, once styrene has been injection molded, the mechanical properties of the resulting plastic are degraded. Thus, if a spool is recycled, ground up into chunks or beads and re-extruded as part of another batch, the degradation in quality can be substantial. Olefinic plastics improve over styrene-based plastics in that olefinic plastics can be completely recyclable. The mechanical properties of an olefinic plastic are virtually identical for reground stock as for virgin stock.
In reels, a 12-inch diameter unit is instructive. Such a spool is usually manufactured of wood. Nevertheless, a plastic spool in 12-inch diameter may also be manufactured with a pair of plastic flanges holding a layered cardboard (paperboard) tube detained therebetween. The flanges are typically bolted together axially to hold the tube within or without a circumferential detent as with wooden reels.
The reels have an additional difficulty when they are dropped during use. The flanges do not stay secured. The flange and tube are often precarious wooden assemblies held together by three or more axial bolts compressing the flanges together. The tube is prone to slip with respect to the flanges, breaking, tilting or otherwise losing its integrity under excessive loads. Such loads result from the impact of dropping onto a floor from a bench height or less. For the largest reels, rolling over or into obstacles or from decks during handling is more likely to be the cause of damage.
Very large cables, having an outside diameter up to several inches is taken up during manufacturing on a very large reel, from two feet to eight feet in diameter. The current state of the art dictates wooden reels comprised of flanges capturing a barrel-like tube of longitudinal slats therebetween. The two flanges are held together by a plurality of long bolts extending therethrough.
Wooden reels are not typically recyclable. A splinter or blemish in a reel can damage insulation on new cable or wire wrapped therearound at the manufacturing plant. Damaged insulation destroys much of the value of a reel of cable or wire. That is, the wire must be spliced, or may have damage extending over several wrapped layers of wire. Splices segmenting the original length of wire wrapped on the reel add costs in labor, reliability, service and the like.
Wood cannot be recycled and reconstructed cost effectively. In addition, the plurality of bolts and nails must be removed with other related metal hardware. The reels do not effectively bum without the labor investment of this dismantling operation.
Also, a wooden reel that is slightly out of adjustment, damaged, or broken, is problematic. A broken reel leaves a large area splintered to damage wire insulation. A reel which is loose will tilt and twist as the slats shift with respect to the flanges.
Steel reels tend to be more frequently recyclable. However, each must be returned in its original form to be reused. Thus, the bulk of transfer is as large as the bulk of original shipment, although the weight is less. Also, steel is heavy, subject to damage by the environment such as by stains, rust, peeling of paint, denting, accumulation of coatings or creation of small burrs on surfaces and comers. For example, when a reel is rolled over a hard surface, sharp objects, grit or rocks tend to raise small burrs on the outer edge of the flange. Similarly, contact with any sharp or hard object can raise burrs on the inside surfaces of the flanges.
As with wooden reels, only to a greater extent, a burr on a steel reel tends to act like a knife, slicing through insulation and ruining wire. Perhaps the most difficult aspect of burrs is that they are hardly detectable at sizes which are nevertheless highly damaging to insulation. Of course the weight and cost of steel reels is another factor in the difficulty of employing them for delivery of cable.
What is needed is a design for large (12 inches greater diameters) and small diameter (typically 6xc2xd-inch outside diameter) plastic spool flanges, which can tolerate the energy of being dropped when fully wrapped with wire. In addition, even in the standard styrene-based plastic spools, a better design is desired. What is needed in large reels of from a foot to eight feet approximately in outside flange diameter is a reel which is dimensionally stable, maintains structural integrity in service and during accidental dropping, which will not fracture or separate at a flange if it is dropped, and which is economically recyclable.
In a large reel, on the order of two to eight feet in diameter, what is needed is a lightweight, high-strength reel. The reel should not tend to damage wire when scratched, gouged, or otherwise having a burr raised on any key surface. Similarly, a large reel should be resilient enough that it does not maintain a permanent set, such as a steel reel will, when damaged. A plastic reel should be formed in a design that resists fracture and of a material which is tough. The material should be flexible enough that a burr will not damage insulation. A large reel should be recyclable. Recycling is most efficient if a reel can be reground near the site of use. Empty reels are more voluminous than they are heavy.
Moreover a design is needed that provides improved toughness by virtue of design, regardless of the toughness of the material. Catastrophic failure of reels and spools limits their applicability within the wire and cable industry. The risk of losing the use of the stranded material held thereon is not to be risked for the cost of using plastic spools and reels.
In view of the foregoing, it is a primary object of the present invention to provide spools and reels and a method of designing them that will optimize strength, stiffness, fracture, distortion, toughness, and so forth at various locations within the flanges for survival of drop tests.
It is an object of the invention to provide various flange designs that can absorb shock or impact loads without completely fracturing.
It is an object of the invention to provide a design of, and method for designing, flanges of spools and reels having controlled fracture and controlled distortion in order to optimize survival of flanges and the integrity of the flange-to-tube transitions in configurations of spools having minimum weight and highest produceability in molding outputs.
It is an object of the invention to provide selective distortion, stiffness, and fracture of a flange in order to protect the integrity of a core or hub region of the flange.
It is an object of the invention to provide an eccentric application of impact loads transmitted from a rim toward a core region of a flange connecting to a tube portion, whether the tube is initially formed integrally or separately from the flange.
It is an object of the invention to provide multiple regions within the web of a flange, with the regions adapted to provide differing material properties, including different sections, moments of inertia, stiffness, strength, toughness, fracture-resistance, fracture-susceptibility, and the like.
It is an object of the invention to provide increased stiffness in the web while employing thinner walls, yet such that impact loads will not separate a rim and web from a core region of a flange, but maintain mechanical integrity of the flange especially in the tube transition region.
The invention solves this multiplicity of problems with flanges for plastic spools and reels formed in a multi-piece structure preferably by molding from olefinic, ABS, styrenic, and other plastics. Some of the designs may be made tough, even when manufactured of styrene-based plastics. The designs are particularly well adapted to manufacture using molded polyethylene and polypropylene or similar olefinic plastics regardless of tube (core) retention methods.
The structures and methods of the invention apply to spools and reels of all sizes. However, a structure that can be injection molded in a 6xc2xd-inch flange diameter may have to be roto-molded (tumble-molded) to produce an eight foot diameter spool or reel. Consistent with the foregoing objects, and in accordance with the invention as embodied and broadly described herein, an apparatus and method are disclosed, in suitable detail to enable one of ordinary skill in the art to make and use the invention.
In one presently preferred embodiment of an apparatus in accordance with the invention, a central tube or core section may be disposed between two flanges. Construction of the core and flange joints may be done in accordance with various approaches known in the art, as well as those articulated in U.S. Pat. No. 5,464,171, incorporated herein by reference.
Nevertheless, a tube may be completely hollow, ribbed or corrugated, itself. Alternatively, tubes may be arranged to fit within cavities formed in flanges, or to fit outside a sleeve protruding inwardly from a flange, or both at once. In certain embodiments, a flange and tube may be molded in a single piece with a mating tube and associated flange being molded in another piece. The two pieces may then be bonded together by a suitable means to provide a complete spool or reel.
Hybrid spools and reels may be formed using different materials for flanges than for tubes (cores). In other embodiments, a single material may be used for both flanges and tubes assembled from two or more parts. In one presently preferred embodiment, a cardboard tube may be adapted to fit over sleeves protruding from integrally formed flanges extending therefrom.
In one embodiment, flanges may be corrugated to provide a multiplicity of beneficial features. Thickness of walls, more complete closure of cavities (on all sides but one, for example), selective fracture resistance and fracture susceptibility, stiffniess, strength, rigidity, a moment of inertia, a section, and so forth may be affected.
Corrugations may be arranged in a spoke-like configuration extending radially from a core or a hub portion of a flange. Alternatively, corrugations may extend radially at uniform or non-uniform circumferential angles. Corrugations may extend circumferentially between orthogonal surfaces thereto or surfaces non-orthogonal thereto in order to optimize weight, strength, stiffniess, toughness, and other significant functionality.
Corrugations may terminate in selective angles with respect to tangents to the hub (core) portion, and at different selected angles with respect to tangents to a rim or outer circumference of a flange. Moreover, an angle of sweep measured between a tangent of a corrugation edge proximate a core and such an angle measured proximate a rim may differ by any suitable number of degrees. Accordingly, corrugations may be formed to direct loads radially between a hub and rim portion of a flange.
Alternatively, corrugations may be arranged to preclude direct transfer of loads normal to any tangents to a hub, rim, or both. Loads may include compression, tension, shear, bending, and so forth. Corrugation surfaces may be designed to provide a selected strength, stiffness, and toughness at any location within a flange. Corrugations may provide axial loading to retain stranded material, even after substantial damage to a flange. Moreover, the balance between strength, stiffniess, and toughness may be designed specifically to be different at different locations within a flange. Accordingly, flanges may be designed specifically to address loading caused by different types of falls, a major source of damage in use.
Eccentric and tangential interception of corrugations by a hub of a flange may be designed to promote absorption of energy of an impact, by distortion, selective fracture, or by rigid survival. However, in certain embodiments, portions of a flange may be designed to fail to a selected extent in a selected region in order to protect other portions of the flange that would result in more costly damage if allowed to fracture.
Thus, for example, outer portions of a flange may be permitted to crush, bend, break, and so forth in order absorb certain loads. The rim having greater circumference, more material may be naturally provided for absorbing such damage. Meanwhile, a hub may be configured to minimize damage, since a hub may be substantially smaller than a rim (outer diameter or outermost portion) of a flange. In one presently preferred embodiment, bending loads may selectively fracture corrugation walls on one axial side, while transferring loads away to other areas. This re-distribution may reduce fractured circumference at the core, maintaining integrity while permitting fracturing of adequate length to absorb shock loads.
Even near a hub, geometries of flanges may promote selective fracture. For example, selected portions of corrugations may be designed to have thicknesses, angles, and loads calculated to cause a fracture of a limited length and direction. Other nearby locations may be configured with geometries, materials, thicknesses, and so forth to virtually preclude fracture in a similar circumstance. Both features, one susceptible to ready fracture at a known location, and one resistant to expected fracture at a nearby location may provide selective fracture for absorption of energy without catastrophic failure. Catastrophic failure may be regarded as a failure that is likely to destroy the contents of a spool or reel, render it otherwise useless due to increased effort to retrieve, or create an impossibility or difficulty of supporting and retrieving stranded materials, and the like.
In other embodiments, circumferential corrugations may be used. Moreover, angled or curved corrugations may be used in combination with one another, or circumferential corrugations, or with surfaces of various configurations in order to optimize fracture toughness, strength, stiffness, etc. In one embodiment, a flange may be subdivided radially to provide portions having greater or lesser resistance to fracture or energy absorption. Corrugations may have axial depth. Axial depth may be constant or variable in a radial, axial, or circumferential direction. Nevertheless, molding considerations may provide or benefit from certain uniformities.
Inner surfaces of flanges, those surfaces in contact with the stranded materials stored thereon, may be smooth or corrugated. Accordingly, distances across corrugations may be uniform or non-uniform in a radial, circumferential, or axial direction. Moreover, a directorix may be defined for each corrugation, and even each surface extending in a more-or-less radial direction. Thus, adjacent surfaces or directrices defining surfaces extending radially but connected circumferentially by orthogonal or other surfaces, may have different angles, and may be angled, curved, both, or alternating.
As a practical matter, inner surfaces or interior surfaces of a spool may desirably be designed to extend circumferentially a greater portion of circumference of a flange at any given radius. Thus, the inner, clear span of a stranded material between axial support surfaces will be a relatively lesser fraction of the overall circumference at any radius. Nevertheless, multiple corrugations having sufficiently high frequency to provide short clear spans may obviate any necessity for non-uniformity in a circumferential expanse of any corrugation on an inner or outer surface of a flange. Likewise, surface liners, such as a paperboard, or re-ground plastics, and other inexpensive materials may be installed during manufacture, or after manufacture, to separate wire or other stranded materials from touching an interior flange surface or from tending to escape axially into corrugations corresponding to exterior flange surfaces.
Various alternative embodiments of corrugated spools and reels may be fabricated to have corrugations in various shapes, orientations, and locations. For example, corrugated core regions associated with the portion of a flange within an outer diameter of a connecting tube may be corrugated in various configurations, just as the outer portion of the flange may be corrugated in various configurations.
The core and outer portion of a flange need not be corrugated in the same manner, the same pattern, the same direction, or with any other similar orientation. Moreover, the core and the outer portion of a reel may be made as separate pieces, and secured together with the same fastener that secures the intervening or connecting tube in place. Alternatively, a different fastener may hold the core and outer portion together, while a tube fastener holds the flange to the tube.
In selected embodiments, a core may not require corrugations, but may have apertures to accommodate the two prongs of tools or a tool such as a stapler. A true stapler has an active prong comprising the head, which delivers the staple, and an inactive or anvil prong, for receiving the staple and bending the ends thereof.
The apertures allow access to a tube by a two-prong or double prong tool (e.g. stapler), and to the portions of a reel flange designed to hold the tube. Access may be provided by an aperture and a recess (part of a corrugation) or by a pair of corrugations located radially inside and radially outside of the tube.
In selected embodiments, cross-sections may be defined to run radially, and thus vary in circumferential dimension along a radius. Cross-sections may be rectangular, trapezoidal, sinusoidal, or of any variety, provided in any other corrugated system. Alternatively, corrugations may be disposed to run with cross-sections normal to a circumferential direction. That is, a corrugation may extend with its own longitudinal direction lying along a circumferential path about a flange, that is, wherein a cavity of a corrugation cross-section appears in the radially and axially extending plane with respect to the flange.